Radial piston machine

ABSTRACT

A radial piston machine wherein the cylinder block is automatically centered on a pintle wherein the high-pressure chamber is flanked by portions of two circumferentially complete sealing rings whose area is smaller than the area of sealing ring portions in the region of the low-pressure chamber and/or wherein the recesses which flank the high- and low-pressure chambers have relatively wide portions in the region of the low-pressure chamber and relatively narrow portions in the region of the highpressure chamber.

United States Patent Nonnenmacher 1 July 8, 1975 [54] RADIAL PISTON MACHINE 2,423,654 7/1947 Leis 91/491 X 336L038 l 1968 O] ff.... 92 S8 [75] inventor: Gerhard Nonnenmacher, Komtal, 3,464,3[6 9;]969 53 91/49: x Germany 3,663,124 5/1972 Schultz 91/491 x [73] Assignee: Robert Bosch G.m.b.H., Stuttgart, FQREIGN PATENTS O APPLICATIONS Germany 958,028 5/1964 United Kingdom 9I/498 [22] Filed: Sept. 24, 1973 1.239.955 7/1971 United Kingdom................... 91/498 [2]] Primary Examiner-Martin P. Schwadron Appl. No.: 399,821

Assistant Examiner-Abraham Hershkovitz [30] Foreign Application Priority Data Attorney, Agent, or FirmMichael S. Striker Oct. 2, I972 Germany 2248316 [57] ABSTRACT US. Cl. 92/121; A radial piston machine h i the yli block is 92/58; 92/72 automatically centered on a pintle wherein the high- [5|] 1|!!- CI. F01!) 13/00 pressure chamber is flanked by portions of two Cir [58] Field Search 92/121 72; cumferentially complete sealing rings whose area is 91,491, 498 smaller than the area of sealing ring portions in the region of the low-pressure chamber and/or wherein the [56] Rderences Cited recesses which flank the highand low-pressure cham- UNITED STATES PATENTS bers have relatively wide portions in the region of the |,9l7,783 7/l933 Vickers 91/486 low-pressure chamber and relatively narrow portions 2,006,880 7/1935 Benedek..... in the region of the high-pressure chamber. 2,023,2l6 12/1935 Benedek..... I D i 2,205,913 6/1940 Stacy 91/49 F x 19 C 5 guns Er]? 7' x 7 1 RADIAL PISTON MACHINE BACKGROUND OF THE INVENTION The present invention relates to radial piston machines in general, and more particularly to improvements in the construction and configuration of pintles on which the cylinder block of a radial piston machine rotates when the machine is used as a pump or motor. Still more particularly, the invention relates to improvements in means for centering the cylinder block on the pintle.

It is known to provide the peripheral surface of the pintle in a radial piston machine with two chambers which extend in the circumferential direction of the pintle and register with successive cylinders of the cylinder block when the machine is in use. One of the chambers is a high-pressure chamber and the other chamber is a low-pressure chamber. The chambers are separated from each other by lands. It is further known to provide the peripheral surface of the pintle with recesses which extend circumferentially and flank the chambers at opposite sides. The recesses are provided between two sealing rings which are bounded by cylindrical surfaces adjacent to the respective portions of the internal surface of the cylinder block.

A drawback of presently known radial piston machines is that the cylinder block is allowed to move radially of the pintle when the machine is in use. Such radial movement is due to the action of pressurized fluid in those cylinders of the cylinder block which travel along the high-pressure chamber of the pintle. As a rule, such action of pressurized fluid in the cylinders is opposed by pressure fields which develop between the peripheral surface of the pintle in the region of the high-pressure chamber and the adjacent portion of the internal surface of the cylinder block. More particularly, such pressure fields develop between the cylinder block and those portions of the sealing rings which flank the high-pressure chamber as well as between the cylinder block and two sealing projections or ribs which flank the high-pressure chamber and are located between the high-pressure chamber and the aforementioned recesses. By properly dimensioning the sealing ribs and rings, one can insure that the force which opposes movements of the cylinder block toward the axis of the pintle in the region of the high-pressure chamber exceeds the force with which pressurized fluid in the cylinders approaching the high-pressure chamber tends to move the cylinder block toward the axis of the pintle. This, however, causes the cylinder block to approach the pintle in the region of the low-pressure chamber which is located diametrically opposite the high-pressure chamber. Consequently, the width of the gap between the internal surface of the cylinder block and the peripheral surface of the pintle increases in the region of the high-pressure chamber which results in excessive leakage of pressurized fluid.

German Offenlegungsschrift No. 1,453,629 discloses a radial piston machine wherein the peripheral surface of the pintle is provided with two endless recesses flanking the two chambers and receiving leak fluid exclusively from the high-pressure chamber. Consequently, the leak fluid generates identical pressure fields not only in the region of sealing rings at both sides of the high-pressure chamber but also in the region of those sealing ribs which flank the high-pressure chamber. It is evident that such pressure fields are incapable of balancing the forces which act on the cylinder block and tend to move it radially of the pintle.

SUMMARY OF THE INVENTION An object of the invention is to provide a radial piston machine with a novel and improved pintle which is constructed, mounted and configurated in such a way that it insures automatic balancing of all forces which act on the cylinder block in the radial direction of the pintle so that the cylinder block is automatically centered on the pintle when the machine is in use.

Another object of the invention is to provide a pintle for use in radial piston machines with novel and improved means for centering the cylinder block thereon.

A further object of the invention is to provide the peripheral surface of the pintle with novel and improved recesses, sealing rings, sealing ribs, grooves, depressions, lands and chambers which insure that the cylinder block is properly centered when the radial piston machine is in use so that losses due to friction and leakage of pressurized fluid are but a small fraction of similar losses in conventional radial piston machines.

An additional object of the invention is to provide novel and improved means for preventing the internal surface of the cylinder block in a radial piston machine from moving away from that portion of the peripheral surface of the pintle which surrounds the high-pressure chamber.

The invention is embodied in a radial piston machine wherein a cylinder block rotates in the interior of a housing around a stationary pintle whereby the pistons in the cylinders of the block move radially inwardly and outwardly under the action of an annular slide block which is adjustable radially of the pintle. More particularly, the invention is embodied in the pintle whose peripheral surface is provided with elongated highpressure and low-pressure chambers extending in the circumferential direction of the pintle and being separated from each other by two lands. In accordance with a feature of the invention, the peripheral surface of the pintle further includes a pair of sealing elements which may constitute circumferentially complete rings extending circumferentially of the pintle at the opposite sides of the chambers and being spaced apart from the chambers, two recesses extending circumferentially of the pintle and each disposed between the chambers and one of the sealing elements, a first pair of sealing projections (e.g., ribs) disposed between the recesses and the high-pressure chamber, and a second pair of sealing projections disposed between the recesses and the lowpressure chamber. The cylinder block is properly centered on the pintle if the area of each sealing element in the region of the high-pressure chamber is less than the area of each sealing element in the region of the low-pressure chamber and/or if the width of the recessesas considered in the axial direction of the pintle-in the region of the low-pressure chamber is greater than the width of the recesses in the region of the highpressure chamber.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved radial piston machine itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a radial piston machine having a pintle which embodies one form of the invention;

FIG. 2 is a fragmentary developed view of the pintle in the radial piston machine of FIG. 1;

FIG. 3 is a fragmentary developed view of a second pintle;

FIG. 4 is a fragmentary developed view of a third pintle; and

FIG. 5 is a transverse sectional view of the third pintle as seen in the direction of arrows from the line V-V of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The radial piston machine of FIG. 1 comprises a housing 1 having a separable cover portion 2 which is provided with a bore 3 for a portion ofa valve or pintle 4. The pintle 4 is held against rotation relative to the housing 1 by a pin 40. A cylinder block 5 which is rotatable on the pintle 4 in the interior of the housing 1 has a plurality of radially extending cylinders 6 for radially movable pistons 7 each having an articulately mounted shoe or head 8 arranged to travel along the cylindrical internal surface of a slide block 9 which controls the length of piston strokes and is adjustable radially of the pintle 4. The slide block 9 is rigid with a nut 10 meshing with a spindle 11 which is rotatable in a bracket 12 of the housing 1 in response to turning of a handwheel 13. A helical spring 14 reacts against the housing 1 and bears against the slide block 9 diametrically opposite the nut 10. The spindle 11 cannot move axially relative to the bracket 12 so that the nut 10 moves the slide block 9 radially of the pintle 4 as soon as the operator turns the handwheel 13.

Each cylinder 6 has a conical inner end portion 6' which tapers toward a port 15 in the cylinder block 5. Successive ports 15 of the cylinder block 5 travel along two elongated chambers 16 and 17 which are provided in the periphery of the pintle 4 and are separated from each other by lands 18, 19. The chambers 16, 17 respectively communicate with axially parallel bores 16', 17' which are machined into the pintle 4. A shaft 105 of the cylinder block 5 is driven by a prime mover (not shown) when the machine is used as a pump. When the machine is used as a motor, the cylinder block 5 drives the shaft 105.

The configuration of the pintle 4 is shown in FIG. 2. The chamber 16 is assumed to constitute a highpressure chamber and the chamber 17 is assumed to constitute a low-pressure chamber. The land 18 is located opposite that piston 7 which reaches its inner end position and the land 19 is located opposite that piston 7 which reaches its outer end position with respect to the cylinder block 5.

The chambers l6, 17 are disposed between two endless recesses 20, 21 which extend in the circumferential direction of the pintle 4. The recess 20 has a relatively wide portion 20' which extends from the central region of the land 18 to the central region of the land 19 and is adjacent to one side of the low-pressure chamber 17. The recess 21 has a similar relatively wide portion 21 which is also adjacent to the chamber 17 and extends from the central region of the land 18 to the central region of the land 19. As shown in FIG. 2, the width of the portions 20', 21' substantially exceeds the width of those portions of the recesses 20, 21 which are adjacent to the high-pressure chamber 16. Relatively narrow sealing ribs or projections 22, 23 respectively separate the narrower portions of the recesses 20, 21 from the chamber 16, and similar sealing projections or ribs 24, 25 respectively separate the wider portions 20', 21' of the recesses 20, 21 from the chamber 17.

The recess 20 is flanked at one side by the sealing ribs 22, 24 and the lands 18, 19, and at the other side by an endless sealing element or ring 26. A similar endless sealing element or ring 27 is outwardly adjacent to the recess 21. The ring 26 extends all the way to the inner end face of the pintle 4 and is provided with an elongated cavity or depression 29 which communicates with the interior of the housing 1. The sealing ring 27 is adjacent to an endless groove 28 which also communicates with the interior of the housing 1. An elongated cavity or depression 30 is provided in the ring 27 adjacent to the groove 28. The depression 29, 30 are substantially aligned with the high-pressure chamber 16 and their length, as considered in the circumferential direction of the pintle 4, equals or closely approximates the length of the chamber 16. The pressure in each of the depressions 29, 30 corresponds to fluid pressure in the interior of the housing 1.

In accordance with a feature of the invention, the width of the portions 20', 21 of the recesses 20, 21 and of the depressions 29, 30 is selected in such a way that the width of the sealing rings 26, 27 in the region of the chamber 17 exceeds the width of these rings in the region of the chamber 16. In other words, the overall area of those portions of the sealing rings 26, 27 which are adjacent to the high-pressure chamber 16 is less than the overall area of the sealing rings 26, 27 in the region of the low-pressure chamber 17.

When the radial piston machine is in use and the cylinder block 5 rotates about the pintle 4, the fluid pressure acting against the inner end portions 6' of those cylinders 6 which travel along the high-pressure chamber 16 tends to move the cylinder block 5 toward the pintle 4. The pressure of fluid in the chamber 16 counteracts such pressure and tends to prevent the cylinder block 5 from approaching the peripheral surface of the pintle. The internal surface of the cylinder block 5 defines with the peripheral surface of the pintle 4 a narrow gap including portions extending along the sealing ribs 22, 23. The fluid in these portions of the gap between the cylinder block 5 and pintle 4 flows from the high-pressure chamber 16 into the adjacent narrower portions of the recesses 22, 23. Such fluid produces pressure fields which are outwardly adjacent to the sealing ribs 22, 23 and assist the fluid pressure in the high-pressure chamber 16 in preventing the cylinder block 5 from approaching the pintle 4. The combined forces furnished by fluid in the chamber 16 and by pressure fields adjacent to the sealing ribs 22, 23 exceed the force which tends to move the adjacent portion of the cylinder block 5 radially toward the axis of the pintle 4. As mentioned above, the force which tends to move the cylinder block 5 radially toward the axis of the pintle 4 develops as a result of fluid pressure acting against the conical inner end portions 6' of those cylinders 6 which travel along the high-pressure chamber 16.

The fluid pressure is constant in each and every portion of the recess 20 or 21. Since the portions 20', 21' of the recesses 20, 21 are wider in the region of the lowpressure chamber 17, the fluid in the portions 20', 21' produces forces which tend to move the cylinder block 5 radially of the pintle 4, i.e., in the same direction as the fluid pressure acting on the conical portions 6 of cylinders 6 in the region of the high-pressure chamber 16. This will be readily appreciated by considering that the portions 20' and 21' of the recesses 20 and 21 are located diametrically opposite the high-pressure chamber 16.

Some pressurized fluid leaks from the recesses 20, 21 along the sealing rings 26, 27 and into the interior of the housing 1. This leads to establishment of pressure fields which are adjacent to the sealing rings 26, 27 and whose distribution is non-symmetrical due to the provision of wider portions 20', 21' of the recesses 20, 21 and also due to the provision of depressions 29, 30 in the sealing rings 26, 27. The resultant of forces gener ated by pressure fields between the internal surface of the cylinder block 5 and the sealing rings 26, 27 tends to move the cylinder block 5 nearer to the pintle 4 in the region of the high-pressure chamber 16. The magnitude of such resultant force depends on the width of the gap between the cylinder block 5 and the pintle 4 in the region of the chamber 16', the width of this gap further determines the fluid pressure in the recesses 20, 2] and hence also the magnitude of pressure fields around the sealing rings 26, 27.

The just discussed dimensioning of the width of portions 20', 21' of the recesses 20, 21 and of the width of the depressions 29, 30 insures that the forces which act upon the cylinder block 5 are balanced so that the cylinder block is automatically centered on the pintle 4. This insures that the friction and losses due to leakage of pressurized fluid are reduced to a minimum. It is clear that a highly satisfactory balancing of forces acting on the cylinder block 5 and/or pintle 4 can be achieved by properly dimensioning the relatively wide portions 20', 21' of the recesses 20, 21 by properly dimensioning the width of the depressions 29, 30.

FIG. 3 illustrates a portion of a second pintle 35 having a high-pressure chamber 36, a low-pressure chamber 37, lands 38, 39, and two circumferentially complete recesses 40, 41 of constant width, as considered in the axial direction of the pintle. The recesses 40, 41 are respectively separated from the chambers 36, 37 by sealing projections or ribs 43, 42 and 44, 45. The two sealing elements or rings are shown at 46 and 47. The sealing ring 46 extends all the way to the inner end face of the pintle 35 and is provided with a substantially U- shaped depression or cavity 49 the major portion of which is aligned with the high-pressure chamber 36 and which has two relatively short portions or legs 50, S1 communicating with the interior of the housing, not shown. The sealing ring 47 is disposed between the recess 40 and a circumferentially complete annular groove 48 which communicates with the interior of the housing. The major portion of a U-shaped cavity or depression 53 in the ring 47 is aligned with the chamber 36 and this cavity has two short portions or legs 54, 55 which communicate with the interior of the housing by way of the groove 48. The major portions of the depressions 49, 53 extend in parallelism with the chamber 36, i.e., in the circumferential direction of the pintle 35. The depression 49 surrounds three sides of a substantially rectangular portion 52 of the sealing ring 46, and the depression 53 surrounds a similar portion 56 of the sealing ring 47. The fourth side of the portion 56 is surrounded by the groove 48.

The fluid pressure in the high-pressure chamber 36 opposes the pressure of fluid in those cylinders of the cylinder block (not shown in FIG. 3) which travel along the chamber 36. The fluid pressure in the chamber 36 is assisted by pressure fields between the internal surface of the cylinder block and the sealing ribs 42, 43. These pressure fields develop as a result of leakage of pressurized fluid from the chamber 36 into the adjacent portions of the recesses 40, 41. The pressure fields tend to reduce the gap between the low-pressure chamber 37 and the adjacent portion of the cylinder block.

The fluid which leaks from the recesses 40, 41 into the interior of the housing produces pressure fields between the internal surface of the cylinder block and the sealing rings 46, 47. However, no such pressure fields develop around the portions 52, 56 of the sealing rings 46, 47, i.e., the distribution of pressure fields in the region of the sealing rings 46, 47 is not symmetrical. This results in the generation of a resultant force which acts in the region of the low-pressure chamber 37 and tends to move the cylinder block in the same direction as the force acting on the inner end portions of cylinders.

The areas of the portions 52, 56 of the sealing rings 46, 47 can be readily selected in such a way that the forces which tend to move the cylinder block radially toward the axis of the pintle 35 are balanced by forces which tend to move the cylinder block away from the axis of the pintle. Thus, the cylinder block remains accurately centered to thus reduce friction and losses due to leakage.

FIGS. 4 and 5 illustrate a portion of a third pintle 60 which is somewhat similar to the pintle 4 but is provided with modified recesses of finite length. One of the recesses includes two arcuate sections 61, 63 which respectively extend along the chambers 16, 17 and a channel-shaped pressure-equalizing section 65 which connects the sections 61, 63 and is machined into the body of the pintle 60 in the region of the land 18. The other recess has two arcuate sections 62, 64 and a channelshaped pressure-equalizing intermediate section 66. The width of the sections 61, 62 (which flank the high-pressure chamber 16) is substantially less than the width of the sections 63, 64 (which flank the lowpressure chamber 17). In all other respects, the pintle 60 is identical with the pintle 4.

The areas of the depressions 29, 30 and sections 63, 64 of the two recesses are again selected in such a way that the areas of the sealing rings 26, 27 in the region of the high-pressure chamber 16 are smaller than in the region of the low-pressure chamber 17.

The pintle 35 of FIG. 3 can be modified by replacing the endless recesses 40, 41 with recesses of finite length each of which has a first section extending along the chamber 36, a second section extending along the chamber 37, and a channel-shaped intermediate section connecting the first and second sections of the respective recess.

An important advantage of the improved pintle is that the cylinder block is automatically centered when the radial piston machine is in use by the simple and inexpensive expedient of making the areas of the sealing ring portions in the region of the high-pressure chamber smaller than in the region of the low-pressure chamber and/or by making the recesses relatively wide in the region of the low-pressure chamber and relatively narrow in the region of the high-pressure chamber.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In a radial piston machine, a pintle for a cylinder block wherein pistons move radially under the action of a slide block in response to rotation of the cylinder block around the pintle in the interior of a housing, said pintle having a peripheral surface provided with highpressure and low-pressure chambers extending in the circumferential direction of said pintle, lands separating said chambers from each other, a pair of sealing ele ments extending circumferentially of said pintle and being spaced apart from opposite sides of said chambers, recesses extending circumferentially of said pintle and each located between said chambers and one of said sealing elements, a first pair of sealing projections disposed between said recesses and said high-pressure chamber, and a second pair of sealing projections disposed between said recesses and said low-pressure chamber, the area of each of said sealing elements in the region of said high-pressure chamber being less than the area of each of said sealing elements in the region of said low-pressure chamber.

2. A pintle as defined in claim 1, wherein said sealing elements are circumferentially complete rings.

3. A pintle as defined in claim 1, wherein said sealing elements are provided with depressions adjacent to said high-pressure chamber and communicating with the interior of the housing.

4. A pintle as defined in claim 3, wherein said depressions are elongated and extend in the circumferential direction of said pintle.

5. A pintle as defined in claim 1, wherein said sealing elements are provided with depressions each having a first portion extending circumferentially of the pintle adjacent to said high-pressure chamber and at least one second portion connecting said first portion with the interior of the housing.

6. A pintle as defined in claim 5, wherein each of said depressions subdivides the respective sealing element into a first portion which is adjacent to the respective recess and a second portion which is separated from the first portion by the respective depression.

7. A pintle as defined in claim 1, wherein at least one of said recesses is a circumferentially complete recess.

8. A pintle as defined in claim 1, wherein each of said recesses comprises a first arcuate section adjacent to said high-pressure chamber, a second arcuate section adjacent to said low-pressure chamber, and a channelshaped intermediate section connecting said first section to said second section.

9. A pintle as defined in claim 1, wherein at least one of said recesses is of finite length.

10. A pintle as defined in claim 1, further comprising an endless groove provided in said peripheral surface and communicating with the interior of the housing, one of said sealing elements being disposed between said groove and the respective recess.

1]. A pintle as defined in claim 1, wherein the width of said recesses as considered in the axial direction of said pintle in the region of said low pressure chamber is greater than in the region of said highpressure chamber.

12. In a radial piston machine, a pintle for a cylinder block wherein pistons move radially under the action of a slide block in response to rotation of the cylinder block around the pintle in the interior of a housing, said pintle having a peripheral surface provided with highpressure and low-pressure chambers extending in the circumferential direction of said pintle, lands separating said chambers from each other, a pair of sealing elements extending circumferentially of said pintle and being spaced apart from opposite sides of said chambers. recesses extending circumferentially of said pintle and each located between said chamber and one of said sealing elements, a first pair of sealing projections disposed between said recesses and said high-pressure chamber and a second pair of sealing projections disposed between said recesses and said low-pressure chamber, the width of said recesses as considered in the axial direction of said pintle in the region of said low pressure chamber being greater than in the region of said high pressure chamber.

13. A pintle as defined in claim 12, wherein said sealing elements are circumferentially complete rings.

14. A pintle as defined in claim 12, wherein said sealing elements are provided with depressions adjacent to said high-pressure chamber and communicating with the interior of the housing.

15. A pintle as defined in claim 14, wherein said depressions are elongated and extend in the circumferential direction of said pintle.

16. A pintle as defined in claim 12, wherein at least one of said recesses is a circumferentially complete recess.

17. A pintle as defined in claim 12, wherein each of said recesses comprises a first arcuate section adjacent to said high-pressure chamber, a second arcuate section adjacent to said low-pressure chamber, and a channel-shaped intermediate section connecting said first section to said second section.

18. A pintle as defined in claim 12, wherein at least one of said recesses is of finite length.

19. A pintle as defined in claim 12, further comprising an endless groove provided in said peripheral surface' and communicating with the interior of the housing, one of said sealing elements being disposed between said groove and the respective recess. 

1. In a radial piston machine, a pintle for a cylinder block wherein pistons move radially under the action of a slide block in response to rotation of the cylinder block around the pintle in the interior of a housing, said pintle having a peripheral surface provided with high-pressure and low-pressure chambers extending in the circumferential direction of said pintle, lands separating said chambers from each other, a pair of sealing elements extending circumferentially of said pintle and being spaced apart from opposite sides of said chambers, recesses extending circumferentially of said pintle and each located between said chambers and one of said sealing elements, a first pair of sealing projections disposed between said recesses and said high-pressure chamber, and a second pair of sealing projections disposed between said recesses and said low-pressure chamber, the area of each of said sealing elements in the region of said high-pressure chamber being less than the area of each of said sealing elements in the region of said low-pressure chamber.
 2. A pintle as defined in claim 1, wherein said sealing elEments are circumferentially complete rings.
 3. A pintle as defined in claim 1, wherein said sealing elements are provided with depressions adjacent to said high-pressure chamber and communicating with the interior of the housing.
 4. A pintle as defined in claim 3, wherein said depressions are elongated and extend in the circumferential direction of said pintle.
 5. A pintle as defined in claim 1, wherein said sealing elements are provided with depressions each having a first portion extending circumferentially of the pintle adjacent to said high-pressure chamber and at least one second portion connecting said first portion with the interior of the housing.
 6. A pintle as defined in claim 5, wherein each of said depressions subdivides the respective sealing element into a first portion which is adjacent to the respective recess and a second portion which is separated from the first portion by the respective depression.
 7. A pintle as defined in claim 1, wherein at least one of said recesses is a circumferentially complete recess.
 8. A pintle as defined in claim 1, wherein each of said recesses comprises a first arcuate section adjacent to said high-pressure chamber, a second arcuate section adjacent to said low-pressure chamber, and a channel-shaped intermediate section connecting said first section to said second section.
 9. A pintle as defined in claim 1, wherein at least one of said recesses is of finite length.
 10. A pintle as defined in claim 1, further comprising an endless groove provided in said peripheral surface and communicating with the interior of the housing, one of said sealing elements being disposed between said groove and the respective recess.
 11. A pintle as defined in claim 1, wherein the width of said recesses - as considered in the axial direction of said pintle -in the region of said low pressure chamber is greater than in the region of said high-pressure chamber.
 12. In a radial piston machine, a pintle for a cylinder block wherein pistons move radially under the action of a slide block in response to rotation of the cylinder block around the pintle in the interior of a housing, said pintle having a peripheral surface provided with high-pressure and low-pressure chambers extending in the circumferential direction of said pintle, lands separating said chambers from each other, a pair of sealing elements extending circumferentially of said pintle and being spaced apart from opposite sides of said chambers, recesses extending circumferentially of said pintle and each located between said chamber and one of said sealing elements, a first pair of sealing projections disposed between said recesses and said high-pressure chamber and a second pair of sealing projections disposed between said recesses and said low-pressure chamber, the width of said recesses - as considered in the axial direction of said pintle - in the region of said low pressure chamber being greater than in the region of said high pressure chamber.
 13. A pintle as defined in claim 12, wherein said sealing elements are circumferentially complete rings.
 14. A pintle as defined in claim 12, wherein said sealing elements are provided with depressions adjacent to said high-pressure chamber and communicating with the interior of the housing.
 15. A pintle as defined in claim 14, wherein said depressions are elongated and extend in the circumferential direction of said pintle.
 16. A pintle as defined in claim 12, wherein at least one of said recesses is a circumferentially complete recess.
 17. A pintle as defined in claim 12, wherein each of said recesses comprises a first arcuate section adjacent to said high-pressure chamber, a second arcuate section adjacent to said low-pressure chamber, and a channel-shaped intermediate section connecting said first section to said second section.
 18. A pintle as defined in claim 12, wherein at least one of said recesses is of finite length.
 19. A pintle aS defined in claim 12, further comprising an endless groove provided in said peripheral surface and communicating with the interior of the housing, one of said sealing elements being disposed between said groove and the respective recess. 